class MathHelper {
    static PI: number = 3.14;
  
    static calculateCircleArea(radius: number): number {
      return this.PI * radius * radius;
    }
  }
  
  console.log(MathHelper.PI); // 输出: 3.14
  console.log(MathHelper.calculateCircleArea(2)); // 输出: 12.56
  